This invention relates generally to optical connectors, and more particularly to dust caps that attach to the optical connector and protect an optical fiber and ferrule from abrasion, dust and debris.
Optical fiber connectors are used to facilitate mating of optical fibers to one another in an end-to-end relationship in order to permit optical energy to be transferred between fibers. Frequently, such connectors include a ferrule for terminating the exposed end of a glass fiber. An optical ferrule is a generally cylindrical tube that is made, for example, from a ceramic material and includes an axial bore for receiving and holding an end portion of the fiber. Nevertheless, the end face of the fiber is exposed to environmental hazards such as dust, debris and abrasion during the manufacture as well as the testing and handling of connectors. So that interconnections between fibers will have low loss, it is important to protect the end face of the optical fiber when it is not in use. Accordingly, it is known to provide a dust cap, or cover, for the end portion of an optical connector, adapter or other body associated with the connector.
One known type of dust cap is disclosed in U.S. Pat. No. 5,363,460 to Marazzi et al. that uses a flexible flap to cap a fiber optic connector to prevent emissions from the connector. The Marazzi flexible flap allows forcible deflection of the flap area, so that a mating connector can be attached to the normally capped connector, and yet when the mating connector is removed, the flap will automatically return to the capping position. According to Marazzi, in addition to preventing the emission radiation, the flap reduces contamination materials, such as dust, from adhering to the end of the optical fiber. However, incorporating such a dust cap into each connector not only increases the cost of the connector but also requires special receptacles for receiving each connector.
Another known type of dust cap is disclosed in U.S. Pat. No. 5,202,949 to Hileman et al. that comprises a base portion and at least one protruding portion extending therefrom, the protruding portion includes a cavity for receiving and capping the ferrule when the dust cap is mounted to the connector. The Hileman dust cap is used with connectors having a retractable body portion that normally surrounds the ferrule when the connector is not in use. The dust cap is permanently joined to the connector via a lanyard, and appears to be frictionally coupled to the connector when the dust cap is in use. Frictional coupling is undesirable because the force required to remove the dust cap from the connector may be too great or too little. It should not fall from the connector during normal handling but still be loose enough to be easily removed. Moreover, it is desirable to completely dissociate the dust cap from the connector during normal operation because of space constraints in a densely packed connection panel.
Accordingly, it is desirable to provide a dust cap for an optical connector that satisfies the conflicting demands of being completely and easily removable from the connector when the user requires removal, and being tightly held to the connector so that it does not become detached during vigorous handling.
A dust cap according to the invention is advantageously used to protect optical fiber(s) within an optical connector from abrasion, dust and debris when the optical connector is not in normal use. The dust cap is a box-like housing having front and back ends and side walls that define a cavity. The back end of the dust cap has an opening into the cavity that is shaped to receive the optical connector. A retaining feature is included within the cavity and is positioned to interlock with a mating feature on the optical connector so that the dust cap will not detach from the connector during vigorous handling. The dust cap further includes a tubular member (boss) that is shaped to receive and enclose the optical fiber, which may be held within a ferrule. The distal end of the tubular member is closed and projects outwardly from the front end of the dust cap. The proximal end of the tubular member projects into the cavity from the front end of the dust cap and has an opening for receiving the fiber. The proximal end forms a reverse trap, which reduces the possibility of dust reaching the end face of the ferrule where the optical fiber is exposed, analogous to a dust-free surface under a book shelf.
In an illustrative embodiment of the invention, the tubular member is recessed within the cavity so that the optical plug will be well aligned with the dust cap before the ferrule enters the tubular member. This prevents the forward end of the ferrule from contacting the proximal end of the tubular member during insertion. Preferably, the distance between the back end of the dust cap and the proximal end of the tubular member is more than five millimeters.
In the illustrative embodiment of the invention, the dust cap is designed to interlock with an LC-type optical plug, which includes a flexible cantilever latch having a pair of shoulders that mate with the retaining feature on the dust cap. The dust cap is easily and completely removed from the connector by merely depressing the latch. In the illustrative embodiment, LC-type connectors and dust caps are attached to the ends of an optical cable.
The dust cap is preferably molded from a thermoplastic material as a one-piece unit, which may be color coded for identification.